A widely used type of electrical circuit comprises an insulating support, such as a polyester film, having an integral tail extending therefrom and having a multiplicity of terminal sites, such as switch sites, on the film. Circuit conductors extend between and among the terminal sites and onto the tail so that they can be connected to further conductors. The conductors and the switch sites are commonly silkscreened on the insulaing support and are of conductive ink although in some cases, electro-deposited conductors are used.
In the design of membrane circuits as described above, it is highly desirable to lay out the circuit such that the conductors need not cross over each other. If crossovers can be avoided, all of the conductors and all of the terminal sites on the film can be produced by a single silkscreening operation. However, if the complexity of the circuit is such that crossovers cannot be avoided, it is necessary to apply an insulating layer to some of the conductors on the film and then carry out a second silk-screening operation to produce the conductors on the insulating film in crossing relationship to other conductors. These added steps greatly increase the manufacturing cost of membrance circuits and are avoided wherever possible.
Even if crossovers are not required in a circuit, the circuit designer attempts to lay out the conductors on the film in as simple a manner as possible so as to have relatively short runs between the terminal sites and ample distance between adjacent conductors so that the manufacturing operation can be carried out easily.
Many circuits produced by the manufacturing methods discussed above are relatively complex and crossovers are required if present circuit design principles are followed. It is also true that relatively complex circuits result involving relatively long conductors on the support and conductors which are very close to each other so that manufacturing difficulties are encountered.
The present invention is directed to the achievement of an improved tail for membrane type circuits which permits simplification of the layout of the circuit as compared with previously known circuit design techniques. The invention is thus directed to a membrane switch tail which will reduce the incidence of crossovers in the circuit and otherwise simplify the circuit.
An electrical circuit in accordance with the invention is of the type comprising an insulating support having a multiplicity of terminal sites thereon. A plurality of circuit conductors extend between and among the terminal sites and connect the terminal sites to each other. A flexible tail extends from the support and the circuit conductors have output terminal portions which are on one surface of the tail. The electrical circuit is characterized in that at least some of the circuit conductors are dual conductors having first and second conductor sections, the first and second conductor sections having first and second output terminal portions on the one surface of the tail. The first and second output terminal portions of each dual conductor are aligned with each other on opposite sides of a fold line and are equidistant from the fold line. The fold line divides the one surface of the tail into first and second tail surface sections. The tail is folded along the fold line so that the first and second tail surface sections are opposed to each other and the first and second output terminal portions of each dual conductor are opposed to, and in alignment with, each other, and the first and second output terminal portions of each dual conductor are connected to each other in the tail.
In accordance with a further embodiment, the plurality of circuit conductors and the flexible tail constitute a first plurality of circuit conductors and a first tail respectively and the circuit has a second plurality of circuit conductors and a second tail. The second plurality of circuit conductors have output terminal portions which are on the one surface of the second tail and at least some of the second circuit conductors being dual conductors having first and second conductor sections. The first and second conductor sections of the second circuit conductors have first and second output terminal portions on the one surface of the second tail, the first and second output terminal portions of each dual conductor of the second circuit conductors being aligned with each other on opposite sides of a second tail fold line and being equidistant from the second tail fold line. The second tail fold line divides the one surface of the second tail into first and second tail surface sections and the second tail is folded along the second tail fold line so that the first and second tail surface sections are opposed to each other and the first and second output terminal portions of each second dual conductor are opposed to, annd in alignment with, each other. The first and second output terminal portions of each dual conductor are conected to each other in the second tail whereby the circuit has first and second folded tails.
In accordance with a further embodiment, the second tail extends towards the first tail and end portions of the first tail and end portions of the second tail are in parallel planes and are in alignment with each other. The first and second output terminal portions on the second tail are on the end portions of the second tail and the first and second output terminal portions on the first tail are on the end portions of the first tail.
In accordance with a further embodiment, the first and second terminal portions of each dual conductor on the first tail are connected to each other by a connecting device which is crimped onto the first tail, and the first and second terminal output portions of each dual conductor on the second tail are connected to each other by a connecting device which is crimped onto the second tail.